In semiconductor-wafer and like manufacturing, conventionally flow controllers that control the flow rate of gas supplied to the chamber are employed. Since problems in the accuracy with which the flow controllers control flow rate give rise to product defects in the semiconductor wafers, flow rate tests are carried out at regular or irregular intervals in order to verify whether or not the flow controller is able to control the flow rate as designed.
Specifically, the test is conducted as follows.
In a case where, for example, a flow rate test is conducted on a thermal mass flow controller (hereinafter termed a “thermal MFC 101”) comprising a sensor section 101a and a control valve 101b, as shown in FIG. 11, a pressure differential mass flow meter (hereinafter termed a “pressure differential MFM 102”) as a testing standard is provided on the downstream side of the thermal MFC 101 under test, and on the upstream side thereof a regulator is provided, each in series. In this case, the pressure differential MFM 102 is realized by actuating a function of the mass flow meter itself, without operating a valve 103V in a pressure differential mass flow controller 103 therein.
Then the flow in a flow channel in between the control valve 101b and the pressure differential MFM 102 is controlled to be a constant flow rate by the control valve 101b of the thermal MFC 101 under test, and after the pressure differential MFM 102 reaches a target pressure at which its operation is stabilized, the test is conducted by comparing an output value from a sensor section in the thermal MFC 101 under test with an output value from the testing-standard pressure differential MFM 102.
It should be noted that the conventional technology just described is implemented to suit conditions at test sites; its disclosure as patent or other literature is not to be found.